There are known various endoscopic apparatuses employing optical heads for visualization of the interior of the body cavity or lumen. Essential parts of such optical head are imaging system and illumination system. The imaging system might comprise an objective lens at the distal end of the endoscope and an eyepiece at the proximal end of the endoscope to observe the interior of the lumen with the eye.
In the modern endoscopic devices the imaging system comprises an imaging optic and a solid state imaging sensor, e.g. in the form of a CCD-chip or CMOS, which transforms the light signals reflected from the object into electric signals, passing to proximal end via electric lines and visually presented, as a real image, on an image reproduction unit outside the endoscope.
The illumination system serves for transmitting light to distal end of the endoscope to illuminate the location to be observed. Such illumination system might comprise external light sources, e.g. xenon or halogen light sources with fiber optic bundle for submitting light energy from light source to endoscope distal tip or internal light sources, e.g. light emitting diodes (LED's) located within the endsocope.
The use of CCD sensors or CMOS and LED's in optical head of an endoscope is relatively new issue, nevertheless one can mention many patents describing endoscopes provided with such optical devices.
An example of an endoscope with LED illumination can be found in Nakashima (U.S. Pat. No. 6,533,722). In this endoscope the LED's are located within the endoscope shaft and at a distal end thereof. The LED's are arranged such that a part of them is seen so as to overlap with the CCD when viewed from the optical axis direction of the imaging system. By virtue of this provision it is possible to reduce the diameter of the distal end of the endoscope.
Another example of an endoscope provided with a CCD chip and LED's is disclosed in Irion (U.S. Pat. No. 6,730,019). In this endoscope the imaging system (fiber bundle or a CCD sensor) is also located within the shaft, while the LED's are arranged at the proximal end of the endoscope outside of the shaft. The LED's are selected in such a manner that they emit light in different spectral ranges to produce additive mixture of the light.
By virtue of this provision the image acquired by the endoscope is colored as faithfully as possible.
Still further examples of endoscopes employing CCD sensor and LED illumination are disclosed in Pacey (U.S. Patent Publication 2001/0023312), Shipp (U.S. Pat. No. 6,449,006), Henzler (U.S. Patent Publication 2002/0143239), Pacey (U.S. Pat. No. 6,655,377), Henzler (U.S. Pat. No. 6,551,240), Dunki-Jacobs (U.S. Patent Publication 2004/0064018), and Sasaki (U.S. Patent Publication 2004/0102680).
The present invention concerns an optical head, in which a CCD or camera or CMOS is employed in the imaging system and several LED's as part of the illuminating system.
Even though the use of a CCD chip or CMOS and LED's brings many advantages, nevertheless the quality of image acquired with such optical system might require improvement. The reason for this is the illumination nonuniformity due to the excessive or insufficient illumination of various locations in the body lumen. The illumination nonuniformity significantly limits the distance along which a good picture can be acquired. The other problem, which arises in the optical heads provided with the LED illumination, is associated with the situation when the longitudinal axis of the optical head is not parallel with the longitudinal axis of the body lumen or cavity. This problem often arises when the doctor displaces the endoscope within the body lumen. As a result of this displacement various locations of the observable area are illuminated with different intensity and it is difficult to acquire good pictures of the whole observed area.
In Avni (U.S. Patent Publication 2003/0032860) is described a video rectoscope equipped with a video camera head which has a color CCD array and several white LED's. The rectosope is manufactured commercially by SightLine Technologies Ltd. as a RectoSight® Disposable Video Rigid Rectoscope. In this optical head each LED is defined by a luminous intensity distribution angle of about 40 degrees. This value of the distribution angle is sufficient for acquiring a good picture along a maximal distance of 50-70 mm. Though such a distance is quite reasonable for a rectoscopic application it might be too short for the colonoscopic procedure.
In Koshikawa (U.S. Pat. No. 6,569,088) is described an endoscope apparatus, in which a problem of excessive halation due to illumination nonuniformity is solved by providing an optical head with two or more types of illumination optical systems having different light strength.
The difference in the light strength is achieved by virtue of several illumination lens systems with a positive or negative power and a diffusion element arranged at the object side. This solution is implemented in an optical head, which employs fiber bundles instead of LED's.
Thus, despite there are known many attempts to devise an endoscope optical head, which uses LED's for illumination, nevertheless there still exists a need for a new and improved optical head, which allows improving the illumination uniformity perceived by CCD or CMOS sensor and thus to increase the distance along which a good picture can be acquired irrespective whether the longitudinal axis of the optical head is parallel or not with the longitudinal axis of the body lumen.
For a better understanding of the present invention as well of its benefits and advantages, reference will now be made to the following description of its embodiments taken in combination with the accompanying drawings.